Method and apparatus for transmitting control signal in radio communication system

ABSTRACT

A method and an apparatus of transmitting a control signal in a wireless communication system is provided. They generate a first-spread sequence by spreading a modulated sequence in the first slot by using a first orthogonal sequence, generate a second-spread sequence by spreading a modulated sequence in the second slot by using a second orthogonal sequence. The first spread sequence and the second spread sequence are transmitted in a subframe. A length of the first orthogonal sequence is shorter than a length of the second orthogonal sequence, the second orthogonal sequence is generated by removing at least one element included in the first orthogonal sequence, and the at least one element to be removed is identical in every index of the first orthogonal sequence.

This application is a 35 U.S.C. §371 National Stage entry ofInternational Application No. PCT/KR2009/002299, filed on Apr. 30, 2009,and claims priority to U.S. Provisional Application No. 61/048,953,filed on Apr. 30, 2008, each of which is hereby incorporated byreference in its entirety as if fully set forth herein.

TECHNICAL FIELD

The present invention relates to wireless communications, and moreparticularly, to a method and apparatus for transmitting a controlsignal in a wireless communication system.

BACKGROUND ART

Wireless communication systems are widely spread all over the world toprovide various types of communication services such as voice or data.In general, the wireless communication system is a multiple accesssystem capable of supporting communication with multiple users bysharing available system resources (e.g., bandwidth, transmission power,etc.). Examples of the multiple access system include a code divisionmultiple access (CDMA) system, a frequency division multiple access(FDMA) system, a time division multiple access (TDMA) system, anorthogonal frequency division multiple access (OFDMA) system, a singlecarrier frequency division multiple access (SC-FDMA) system, etc.

SC-FDMA has almost the same complexity with OFDMA, and has a lowerpeak-to-average power ratio (PAPR) due to a single carrier property.Since the lower PAPR is advantageous to a user equipment in terms oftransmit power efficiency, the SC-FDMA is adopted in uplink transmissionin 3^(rd) generation partnership project (3GPP) long term evolution(LTE) as disclosed in the section 5 of 3GPP TS 36.211 V8.0.0 (2007-09)“Technical Specification Group Radio Access Network; Evolved UniversalTerrestrial Radio Access (E-UTRA); Physical channels and modulation(Release 8)”.

Meanwhile, various uplink control signals are transmitted through anuplink control channel. Examples of the uplink control signal include anacknowledgement (ACK)/not-acknowledgement (NACK) signal for performinghybrid automatic repeat request (HARQ), a channel quality indicator(CQI) for indicating downlink channel quality, a scheduling request (SR)for requesting resource allocation for uplink transmission, etc.

When an error occurs in transmission of the uplink control signal, thewireless communication system may experience overall performancedeterioration, and thus the uplink control signal needs to betransmitted with high reliability. In order to improve systemperformance, there is a need for a method capable of effectivelytransmitting the uplink control signal.

DISCLOSURE Technical Problem

The present invention provides a method and apparatus for transmitting acontrol signal by using an orthogonal sequence.

Technical Solution

In an aspect, a method of transmitting a control signal in a subframecomprising a first slot and a second slot in a time domain in a wirelesscommunication system is provided. The method comprises generating acyclically shifted sequence by cyclically shifting a base sequence by acyclic shift amount, generating a modulated sequence on the basis of amodulation symbol representing the control signal and the cyclicallyshifted sequence, generating a first-spread sequence by spreading themodulated sequence in the first slot by using a first orthogonalsequence, generating a second-spread sequence by spreading the modulatedsequence in the second slot by using a second orthogonal sequence andtransmitting the first spread sequence and the second spread sequence inthe subframe. A length of the first orthogonal sequence is shorter thana length of the second orthogonal sequence, the second orthogonalsequence is generated by removing at least one element included in thefirst orthogonal sequence, and the at least one element to be removed isidentical in every index of the first orthogonal sequence.

The first orthogonal sequence is selected from sequences [+1 +1 +1 +1],[−1 +1 −1 +1], and [+1 −1 −1 +1] each of which has a length of 4, andthe second orthogonal sequence is selected from sequences [+1 +1 +1],[−1 +1 −1], and [+1 −1 −1] each of which has a length of 3

The first orthogonal sequence is selected from sequences [−1 −1 +1 +1],[−1 +1 −1 +1], and [+1 −1 −1 +1] each of which has a length of 4, andthe second orthogonal sequence is selected from sequences [−1 −1 +1],[−1 +1 −1], and [+1 −1 −1] each of which has a length of 3.

The control signal is an acknowledgement (ACK)/not-acknowledgement(NACK) signal for hybrid automatic repeat request (HARQ).

In another aspect, an apparatus for wireless communication comprises aradio frequency (RF) unit for transmitting a radio signal and aprocessor coupled to the RF unit, wherein the processor is configuredfor generating a cyclically shifted sequence by cyclically shifting abase sequence by a cyclic shift amount, generating a modulated sequenceon the basis of a modulation symbol representing a control signal andthe cyclically shifted sequence, generating a first-spread sequence byspreading the modulated sequence in a first slot by using a firstorthogonal sequence, generating a second-spread sequence by spreadingthe modulated sequence in a second slot by using a second orthogonalsequence and transmitting the first spread sequence and the secondspread sequence in the subframe that includes the first slo and thesecond slot, wherein a length of the first orthogonal sequence isshorter than a length of the second orthogonal sequence, the secondorthogonal sequence is generated by removing at least one elementincluded in the first orthogonal sequence, and the at least one elementto be removed is identical in every index of the first orthogonalsequence.

Advantageous Effects

System performance can be improved by increasing reliability ontransmission of an uplink control signal.

DESCRIPTION OF DRAWINGS

FIG. 1 shows a wireless communication system.

FIG. 2 shows DL HARQ and CQI transmission.

FIG. 3 shows UL transmission.

FIG. 4 shows a structure of a radio frame in 3GPP LTE.

FIG. 5 is a diagram showing an example of a resource grid for one ULslot.

FIG. 6 shows a structure of a UL subframe.

FIG. 7 shows a base sequence r(n) and a cyclically shifted sequence r(n,a).

FIG. 8 shows a PUCCH structure used in transmission of an ACK/NACKsignal when using a normal CP.

FIG. 9 shows a PUCCH structure used in transmission of an ACK/NACKsignal when using an extended CP.

FIG. 10 shows transmission of an SRS in a subframe.

FIG. 11 shows a PUCCH format in which a last SC-FDMA symbol ispunctured.

FIG. 12 is a block diagram showing an apparatus for wirelesscommunication for implementing an embodiment of the present invention.

MODE FOR INVENTION

The technology described below can be used in various wirelesscommunication systems such as code division multiple access (CDMA),frequency division multiple access (FDMA), time division multiple access(TDMA), orthogonal frequency division multiple access (OFDMA), singlecarrier frequency division multiple access (SC-FDMA), etc. The CDMA canbe implemented with a radio technology such as universal terrestrialradio access (UTRA) or CDMA-2000. The TDMA can be implemented with aradio technology such as global system for mobile communications(GSM)/general packet ratio service (GPRS)/enhanced data rate for GSMevolution (EDGE). The OFDMA can be implemented with a radio technologysuch as institute of electrical and electronics engineers (IEEE) 802.11(Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802-20, evolved UTRA (E-UTRA), etc.The UTRA is a part of a universal mobile telecommunication system(UMTS). 3^(rd) generation partnership project (3GPP) long term evolution(LTE) is a part of an evolved UMTS (E-UMTS) using the E-UTRA. The 3GPPLTE uses the OFDMA in a downlink and uses the SC-FDMA in an uplink.LTE-advance (LTE-A) is an evolution of the 3GPP LTE.

For clarity of explanation, the following description will focus on the3GPP LTE/LTE-A. However, technical features of the present invention arenot limited thereto.

FIG. 1 shows a wireless communication system. A wireless communicationsystem 10 includes at least one base station (BS) 11. Respective BSs 11provide communication services to specific geographical regions(generally referred to as cells) 15 a, 15 b, and 15 c. The cell can bedivided into a plurality of regions (referred to as sectors). A userequipment (UE) 12 may be fixed or mobile, and may be referred to asanother terminology, such as a mobile station (MS), a user terminal(UT), a subscriber station (SS), a wireless device, a personal digitalassistant (PDA), a wireless modem, a handheld device, etc. The BS 11 isgenerally a fixed station that communicates with the UE 12 and may bereferred to as another terminology, such as an evolved node-B (eNB), abase transceiver system (BTS), an access point, etc.

Hereinafter, a downlink (DL) implies communication from the BS to theUE, and an uplink (UL) implies communication from the UE to the BS. Inthe DL, a transmitter may be a part of the BS, and a receiver may be apart of the UE. In the UL, the transmitter may be a part of the UE, andthe receiver may be a part of the BS.

The wireless communication system can support UL and/or DL hybridautomatic repeat request (HARQ). In addition, a channel qualityindicator (CQI) can be used for link adaptation.

FIG. 2 shows DL HARQ and CQI transmission. Upon receiving DL data 51from a BS, a UE transmits an acknowledgement (ACK)/not-acknowledgement(NACK) signal 55 for HARQ after a specific time elapses. The ACK/NACKsignal 55 corresponds to an ACK signal when the DL data is successfullydecoded, and corresponds to a NACK signal when the DL data fails indecoding. Upon receiving the NACK signal, the BS can transmit the DLdata until the ACK signal is received or until retransmission isperformed up to a maximum number of retransmission attempts. Atransmission time of the ACK/NACK signal 55 for the DL data 51 orresource allocation can be dynamically reported by the BS by usingsignaling, or can be pre-agreed according to the transmission time ofthe DL data or the resource allocation. For example, when the DL data 51is received in an n^(th) subframe, the UE can feed back the ACK/NACKsignal in an (n+4)^(th) subframe.

The UE may measure a DL channel state and report a CQI 60 to the BSperiodically and/or non-periodically. The BS may use the CQI 60 in DLscheduling. The BS may report information on a transmission time of theCQI 60 or resource allocation to the UE.

FIG. 3 shows UL transmission. For the uplink transmission, a UE firsttransmits a scheduling request (SR) 110 to a BS. The SR 110 is used whenthe UE requests the BS to allocate UL radio resources, and is a sort ofpreliminary information exchange for data exchange. In order for the UEto transmit UL data 130 to the BS, the UE firsts requests allocation ofthe radio resources by using the SR 110.

In response to the SR 110, the BS sends a UL grant 120 to the UE. The ULgrant 120 includes information on UL radio resource allocation. The UEtransmits UL data 130 by using the allocated UL radio resource.

As shown in FIG. 2 and FIG. 3, the UE can transmit a UL control signalsuch as an ACK/NACK signal, a CQI, and an SR in a given subframe. A typeor size of the control signal may vary depending on a system, andtechnical features of the present invention are not limited thereto.

FIG. 4 shows a structure of a radio frame in 3GPP LTE. The radio frameconsists of 10 subframes. One subframe consists of 2 slots. A timerequired for transmitting one subframe is defined as a transmission timeinterval (TTI). For example, one subframe may have a length of 1millisecond (ms), and one slot may have a length of 0.5 ms.

One slot includes a plurality of SC-FDMA symbols in a time domain andincludes a plurality of resource blocks (RBs) in a frequency domain.Since 3GPP LTE uses SC-FDMA in UL, the SC-FDMA symbol is forrepresenting one symbol period, and can be referred to as an OFDMAsymbol or a symbol period according to a system. The RB includes aplurality of contiguous subcarriers in one slot in a resource allocationunit.

The structure of the radio frame is for exemplary purposes only, and thenumber of subframes included in the radio frame or the number of slotsincluded in the subframe and the number of SC-FDMA symbols included inthe slot can change variously.

FIG. 5 is a diagram showing an example of a resource grid for one ULslot. The UL slot includes a plurality of SC-FDMA symbols in a timedomain and includes a plurality of RBs in a frequency domain. Althoughit is described herein that one UL slot includes 7 SC-FDMA symbols andone RB includes 12 subcarriers, the present invention is not limitedthereto. The number N^(UL) of RBs included in the UL slot depends on aUL bandwidth defined in a cell.

Each element on the resource grid is referred to as a resource element.One RB includes 12×7 resource elements. The resource element on theresource grid can be identified by an index pair (k, l) within the slot.Herein, k(k=0, . . . , N^(UL)×12−1) denotes a subcarrier index in thefrequency domain, and l(l=0, . . . , 6) denotes an SC-FDMA symbol indexin the time domain.

Although it is described herein that one RB includes 7×12 resourceelements consisting of 7 SC-FDMA symbols in the time domain and 12subcarriers in the frequency domain for example, the number of SC-FDMAsymbols and the number of subcarriers in the RB are not limited thereto.Thus, the number of subcarriers or the number of SC-FDMA symbolsincluded in the RB may change variously. The number of SC-FDMA symbolsmay change depending on a cyclic prefix (CP) length. For example, whenusing a normal CP, the number of SC-FDMA symbols included in one slot is7, and when using an extended CP, the number of SC-FDMA symbols includedin one slot is 6.

FIG. 6 shows a structure of a UL subframe. The UL subframe can bedivided into a control region and a data region in a frequency domain.The control region is allocated with a physical uplink control channel(PUCCH) for carrying UL control information. The data region isallocated with a physical uplink shared channel (PUSCH) for carryinguser data. To maintain a single carrier property, one UE may notsimultaneously transmit the PUCCH and the PUSCH.

The PUCCH for one UE is allocated in an RB pair. RBs belonging to the RBpair occupy different subcarriers in each of two slots. This is calledthat the RB pair allocated to the PUCCH is frequency-hopped in a slotboundary. m is a location index indicating a frequency-domain locationof an RB allocated to the PUCCH in the subframe. In the figure, thePUCCH is configured through a region having the same m in the controlregion included in the subframe, and one PUCCH occupies differentfrequency regions in a 1^(st) slot and a 2^(nd) slot.

The PUCCH can support multiple formats. That is, a UL control signalhaving a different number of bits for each subframe can be transmittedaccording to a modulation scheme. For example, when using binary phaseshift keying (BPSK), a 1-bit UL control signal can be transmittedthrough the PUCCH, and when using quadrature phase shift keying (QPSK),a 2-bit UL control signal can be transmitted through the PUCCH.

Now, transmission of a control signal through a PUCCH will be described.

The control signal can be transmitted using a cyclically shiftedsequence. The cyclically shifted sequence can be generated by cyclicallyshifting a base sequence by a specific cyclic shift (CS) amount. Varioustypes of sequences can be used as the base sequence. For example, awell-known sequence such as a pseudo noise (PN) sequence and aZadoff-Chu (ZC) sequence can be used as the base sequence.Alternatively, when one RB includes 12 sub-carriers, the followingsequence having a length of 12 can be used as the base sequence.r _(i)(n)=e ^(jb(n)π/4)  [Equation 1]

Herein, iε {0, 1, . . . , 29} denotes a root index, and n denotes anelement index in the range of 0≦n≦N−1, where N is a sequence length. Adifferent base sequence is defined according to a different root index.When N=12, b(n) can be defined by the following Table.

TABLE 1 i b(0), . . . , b(11) 0 −1 1 3 — 3 3 1 1 3 1 — 3 1 1 1 3 3 3 — 1— — 1 — 3 2 1 1 — — — — — — 1 — 1 −1 3 −1 1 1 1 1 — — — 1 — 3 −1 4 −1 31 — 1 — — — 1 — 1 3 5 1 — 3 — — 1 1 — — 3 — 1 6 −1 3 — — — 3 1 — 3 3 — 17 −3 — — — 1 — 3 — 1 — 3 1 8 1 — 3 1 — — — 1 1 3 — 1 9 1 — — 3 3 — — 1 11 1 1 10 −1 3 — 1 1 — — — — — 3 −1 11 3 1 — — 3 3 — 1 3 1 3 3 12 1 — 1 1— 1 1 1 — — — 1 13 3 3 — 3 — 1 1 3 — — 3 3 14 −3 1 — — — 3 1 3 3 3 — 115 3 — 1 — — — 1 1 3 1 — −3 16 1 3 1 — 1 3 3 3 — — 3 −1 17 −3 1 1 3 — 3— — 3 1 3 −1 18 −3 3 1 1 — 1 — — — — 1 −3 19 −1 3 1 3 1 — — 3 — — — −120 −1 — 1 1 1 1 3 1 — 1 — −1 21 −1 3 — 1 — — — — — 1 — −3 22 1 1 — — — —— 3 — 1 — 3 23 1 1 — — — — 1 — 1 3 — 1 24 1 1 3 1 3 3 — 1 — — — 1 25 1 —3 3 1 3 3 1 — — — 3 26 1 3 — — 3 — 1 — — 3 — −3 27 −3 — — — — 3 1 — 1 3— −3 28 −1 3 — 3 — 3 3 — 3 3 — −1 29 3 — — — — — — 3 — 3 1 −1

A base sequence r(n) can be cyclically shifted as follows.r(n,a)=r((n+a)mod N),for n=0, . . . ,N−1  [Equation 2]

Herein, ‘a’ denotes a CS amount, and ‘mod’ denotes a modulo operation.The number of available CSs varies depending on a CS unit. If the CS ispossible in a unit of one subcarrier (or one element), ‘a’ can be anyvalue in the range of 0 to N−1, and the number of available CSs is N.Alternatively, if the CS is possible in a unit of 2 subcarriers, ‘a’ canbe any value of {0, 2, 4, . . . , N−1}, and the number of available CSsis N/2.

Hereinafter, the available CS of the base sequence denotes a CS that canbe derived from the base sequence according to a CS unit. For example,if the base sequence has a length of 12 and the CS unit is 1, the totalnumber of available CSs of the base sequence is 12. Alternatively, ifthe base sequence has a length of 12 and the CS unit is 6, the totalnumber of available CSs of the base sequence is 6.

FIG. 7 shows a base sequence r(n) and a cyclically shifted sequence r(n,a). A base sequence r(0) having a length of N consists of N elementsfrom r(0) to r(N−1). The cyclically shifted sequence r(n, a) isgenerated by cyclically shifting N elements from r(0) to r(N−1) by a CSamount ‘a’. That is, r(0) to r(N−a−1) are mapped from a subcarrier index‘a’, and r(N−a) to r(N−1) are shifted to a first part of the cyclicallyshifted sequence r(n. a).

FIG. 8 shows a PUCCH structure used in transmission of an ACK/NACKsignal when using a normal CP. Among 7 SC-FDMA symbols included in oneslot, a reference signal (RS) is carried on 3 SC-FDMA symbols, and theACK/NACK signal is carried on the remaining 4 SC-FDMA symbols. The RS iscarried on 3 contiguous SC-FDMA symbols. In this case, the location andthe number of symbols used in the RS may vary, and accordingly, thelocation and the number of symbols used in the ACK/NACK signal may alsovary.

To transmit the ACK/NACK signal, a 2-bit ACK/NACK signal isQPSK-modulated to generate one modulation symbol d(0). A modulatedsequence m(n) is generated based on the modulation symbol d(0) and thecyclically shifted sequence r(n, a). The cyclically shifted sequencer(n, a) is multiplied by the modulation symbol to generate the followingmodulated sequence m(n).m(n)=d(0)r(n,a)  [Equation 3]

A CS amount of the cyclically shifted sequence r(n, a) may vary for eachSC-FDMA symbol or may be identical in each SC-FDMA symbol. Although itis described herein that a CS amount ‘a’ is set to 0, 1, 2, and 3sequentially for 4 SC-FDMA symbols in one slot, this is for exemplarypurposes only.

In addition, to increase a UE capacity, the modulated sequence can bespread by using an orthogonal sequence for each slot. Herein, it isshown that a modulated sequence y(n) is spread by using an orthogonalsequence w_(i)(k) which has a spreading factor K=4 for 4 SC-FDMA symbolson which a control signal is carried in each slot.

The following sequence can be used based on the orthogonal sequencew_(i)(k) (where i is a sequence index and 0≦k≦K−1) of the spread factorK=4.

TABLE 2 Sequence index [w(0), w(1), w(2), w(3)] 0 [+1 +1 +1 +1] 1 [+1 −1+1 −1] 2 [+1 −1 −1 +1]

An ACK/NACK signal is not limited to 2 bits, and thus may consist of 1bit or more bits. A modulation scheme is not limited to QPSK, and thusBPSK or a higher-order modulation scheme can also be used. For example,one modulation symbol is generated using BPSK modulation for a 1-bitACK/NACK signal, and a modulated sequence can be generated based on amodulation symbol and a cyclically shifted sequence.

An RS can be generated based on an orthogonal sequence and a cyclicallyshifted sequence generated from the same base sequence as the ACK/NACKsignal. That is, the cyclically shifted sequence can be used as the RSby spreading it using the orthogonal sequence w_(i)(k) having a spreadfactor K=3. For the spread of the RS transmitted across 3 SC-FDMAsymbols, the following sequence can be used as the orthogonal sequencew_(i)(k) having the spread factor K=3 (where i is a sequence index and0≦k≦K−1).

TABLE 3 Sequence index [w(0), w(1), w(2)] 0 [1 1 1] 1 [1 e^(j2π/3)e^(j4π/3)] 2 [1 e^(j4π/3) e^(j2π/3)]

Meanwhile, the same structure as the PUCCH for transmission of theACK/NACK signal can be used for SR transmission. Since an SR can beknown only by the presence/absence of PUCCH transmission, a specificvalue, e.g., d(0)=1, can be used as the modulation symbol. The BS candistinguish the SR or the ACK/NACK signal by using a CS index of thebase sequence. That is, when using a sequence cyclically shifted by a CSallocated for the SR, transmission of the SR is recognized, and whenusing a sequence cyclically shifted by a CS allocated for the ACK/NACKsignal, the ACK/NACK signal is recognized.

FIG. 9 shows a PUCCH structure used in transmission of an ACK/NACKsignal when using an extended CP. Each of a 1^(st) slot and a 2^(nd)slot includes 6 SC-FDMA symbols. Among the 6 SC-FDMA symbols of eachslot, an RS is carried on 2 SC-FDMA symbols, and a control signal iscarried on the remaining 4 SC-FDMA symbols. The control signal is spreadthrough an orthogonal sequence having a length of 4, and the RS isspread through an orthogonal sequence having a length of 2.

The PUCCH structure configured as shown in FIG. 8 and FIG. 9 does notconsider a case where at least one SC-FDMA symbol is punctured. Forexample, transmission of a sounding reference signal (SRS) is taken intoaccount. The SRS is a reference signal transmitted by a UE to a BS forUL scheduling. By distinguishing from the SRS, a reference signal usedto demodulate a control signal or data on the PUCCH or PUSCH is referredto as a demodulation (DM) reference signal. Hereinafter, the referencesignal is the DM reference signal unless otherwise specified.

FIG. 10 shows transmission of an SRS in a subframe. The SRS istransmitted in a last SC-FDMA symbol of the subframe. In this case, thelast SC-FDMA symbol used in transmission of the SRS is punctured in thePUCCH structure. An SC-FDMA symbol on which the SRS is transmitted isreferred to as a sounding symbol. Herein, a last SC-FDMA symbol among 14SC-FDMA symbols constituting the subframe is a sounding symbol, but thisis for exemplary purposes only, and thus the location and the number ofsounding symbols in the subframe can change variously. The SRS may betransmitted across a full band or may be transmitted in some parts ofthe full band. A UE can transmit the SRS periodically ornon-periodically.

FIG. 11 shows a PUCCH format in which a last SC-FDMA symbol ispunctured. In a 1^(st) slot, since an ACK/NACK signal is transmitted in4 SC-FDMA symbols, spreading is performed through a 1^(st) orthogonalsequence [w(0), w(1), w(2), w(3)] having a length of 4. In a 2^(nd)slot, the ACK/NACK signal is transmitted in 3 SC-FDMA symbols due to apunctured symbol, and thus a 2^(nd) orthogonal sequence [w(0), w(1),w(2)] having a length of 3 excluding an element w(3) is used. When the1^(st) orthogonal sequence having a length of 4 of Table 2 is used inthe 1^(st) slot, [+1, +1, +1], [+1, −1, +1], and [+1, −1, −1] can berespectively used as 2^(nd) sequences w′₀, w′₁, and w′₂ having a lengthof 3. One of the sequences w′₀, w′₁, and w′₂ is selected as the 2^(nd)orthogonal sequence in the 2^(nd) slot.

However, a cross correlation value of the sequence w′₀ and the sequencew′₁ is 1, a cross correlation value of the sequence w′₁ and the sequencew′₂ is 1, and a cross correlation value of the sequence w′₀ and thesequence w′₂ is −1. Therefore, a Euclidian distance is not constant ineach sequence. This may result in performance deterioration in detectionof the sequence. By reference, in the sequences w₀, w₁, and w₂ having alength of 4 in Table 2, a cross correlation value of the sequences w₀and w₁, the sequences w₁ and w₂, and the sequences w₀ and w₂ arerespectively, 0, 0 and 0.

The conventional PUCCH structure may not consider a case where anySC-FDMA symbol is punctured, and thus detection performance maydeteriorate when a PUCCH is spread with an orthogonal sequence.

In one embodiment, to minimize performance deterioration of theorthogonal sequence, it is proposed to use one orthogonal sequenceselected from sequences shown in the following table.

TABLE 4 Sequence index [w(0), w(1), w(2), w(3)] 0 [+1 +1 +1 +1] 1 [−1 +1−1 +1] 2 [+1 −1 −1 +1]

In the 1^(st) sequences w₀, w₁, and w₂ having a length of 4 in the aboveTable, a cross correlation value of the sequences w₀ and w₁, thesequences w₁ and w₂, and the sequences w₀ and w₂ are respectively 0, 0,and 0. 2^(nd) sequences w′₀, w′₁, and w′₂ having a length of 3 obtainedby puncturing w(3) are [+1, +1, +1], [−1, +1, −1], and [+1, −1, −1]. Thecross correlation value of the sequence w′₀ and the sequence w′₁ is −1,the cross correlation value of the sequence w′₁ and the sequence w′₂ is−1, and the cross correlation value of the sequence w′₀ and the sequencew′₂ is −1, and thus a distance between sequences becomes constant.

In order to generate the 2^(nd) orthogonal sequence having a length of 3from the 1^(st) orthogonal sequence having a length of 4 in Table 4, the2^(nd) orthogonal sequence is generated by removing at least one elementincluded in the 1^(st) orthogonal sequence. The at least one element tobe removed is identical in each index of the 1^(st) orthogonal sequence.That is, an element w(3) corresponding to a punctured symbol in eachsequence index is identical in the 1^(st) orthogonal sequence in Table4. When the identical element w(3) is removed, the remaining elementscan be configured to have a constant cross correlation, so thatdetection performance of a control signal is increased in a receiver.

In another embodiment, to minimize performance deterioration of anorthogonal sequence, it is proposed to use one orthogonal sequenceselected from sequences as shown in the following Table.

TABLE 5 Sequence index [w(0), w(1), w(2), w(3)] 0 [−1 −1 +1 +1] 1 [−1 +1−1 +1] 2 [+1 −1 −1 +1]

In order to generate the 2^(nd) orthogonal sequence having a length of 3from the 1^(st) orthogonal sequence having a length of 4 in Table 5, the2^(nd) orthogonal sequence is generated by removing at least one elementincluded in the 1^(st) orthogonal sequence. The at least one element tobe removed is identical in each index of the 1^(st) orthogonal sequence.That is, an element w(3) corresponding to a punctured symbol in eachsequence index is identical in the 1^(st) orthogonal sequence in Table5. When the identical element w(3) is removed, the remaining elementscan be configured to have a constant cross correlation, so thatdetection performance of a control signal is increased in a receiver.

The sequence of Table 4 and Table 5 above can be selectively used onlyin a subframe in which an SC-FDMA symbol is punctured. In a subframe inwhich no SC-FDMA symbol is punctured, the orthogonal sequence of Table 2may be used, and in a subframe in which there is an SC-FDMA symbol to bepunctured, the orthogonal sequence of Table 4 or Table 5 may be used.

Although it is proposed in Table 4 and Table 5 above that the existingorthogonal sequence is changed, the sequence of Table 2 may be directlyor reversely used in a 1^(st) slot in which no SC-FDMA symbol ispunctured, and a sequence having a length of 3 may be used as shown inthe following Table in a 2^(nd) slot in which there is an SC-FDMA symbolto be punctured.

TABLE 6 Sequence index [w(0), w(1), w(2)] 0 [+1 +1 +1] 1 [−1 +1 −1] 2[+1 −1 −1]

Alternatively, a sequence having a length of 3 as shown in the followingTable can be used in the 2^(nd) slot in which there is an SC-FDMA symbolto be punctured.

TABLE 7 Sequence index [w(0), w(1), w(2)] 0 [−1 −1 +1] 1 [−1 +1 −1] 2[+1 −1 −1]

In the proposed Tables, an order of sequences based on each sequenceindex is for exemplary purposes only, and thus may change. For example,in Table 4, a sequence corresponding to a sequence index 1 may be [+1 −1−1 +1], and a sequence corresponding to a sequence index 2 may be [−1 +1−1 +1].

FIG. 12 is a block diagram showing an apparatus for wirelesscommunication for implementing an embodiment of the present invention.The apparatus may be a part of a UE. An apparatus 500 for wirelesscommunication includes a processor 510 and a radio frequency (RF) unit520. The RF unit 520 is coupled to the processor 510, and transmitsand/or receives a radio signal. The processor 510 transmits a UL controlsignal to a BS. The processor 510 transmits the UL control signal on aPUCCH and by using configuration of a PUCCH according to theaforementioned embodiment.

The present invention can be implemented with hardware, software, orcombination thereof. In hardware implementation, the present inventioncan be implemented with one of an application specific integratedcircuit (ASIC), a digital signal processor (DSP), a programmable logicdevice (PLD), a field programmable gate array (FPGA), a processor, acontroller, a microprocessor, other electronic units, and combinationthereof, which are designed to perform the aforementioned functions. Insoftware implementation, the present invention can be implemented with amodule for performing the aforementioned functions. Software is storablein a memory unit and executed by the processor. Various means widelyknown to those skilled in the art can be used as the memory unit or theprocessor.

While the present invention has been particularly shown and describedwith reference to exemplary embodiments thereof, it will be understoodby those skilled in the art that various changes in form and details maybe made therein without departing from the spirit and scope of theinvention as defined by the appended claims. The exemplary embodimentsshould be considered in descriptive sense only and not for purposes oflimitation. Therefore, the scope of the invention is defined not by thedetailed description of the invention but by the appended claims, andall differences within the scope will be construed as being included inthe present invention.

The invention claimed is:
 1. A method of transmitting a control signalin a subframe comprising a first slot and a second slot in a time domainin a wireless communication system, the method comprising: generating acyclically shifted sequence by cyclically shifting a base sequence by acyclic shift amount; generating a modulated sequence on the basis of amodulation symbol representing the control signal and the cyclicallyshifted sequence; generating a first-spread sequence by spreading themodulated sequence in the first slot by using a first orthogonalsequence; generating a second-spread sequence by spreading the modulatedsequence in the second slot by using a second orthogonal sequence; andtransmitting the first spread sequence and the second spread sequence inthe subframe, wherein a length of the second orthogonal sequence isshorter than a length of the first orthogonal sequence, the secondorthogonal sequence is generated by removing at least one elementincluded in the first orthogonal sequence, and the at least one elementto be removed is identical in every index of the first orthogonalsequence, and wherein the length of the first orthogonal sequence is 4,and the length of the second orthogonal sequence is
 3. 2. The method ofclaim 1, wherein the first orthogonal sequence is selected fromsequences [+1 +1 +1 +1], [−1 +1 −1 +1], and [+1 −1 −1 +1] each of whichhas a length of 4, and the second orthogonal sequence is selected fromsequences [+1 +1 +1], [−1 +1 −1], and [+1 −1 −1] each of which has alength of
 3. 3. The method of claim 1, wherein the first orthogonalsequence is selected from sequences [−1 −1 +1 +1], [−1 +1 −1 +1], and[+1 −1 −1 +1] each of which has a length of 4, and the second orthogonalsequence is selected from sequences [−1 −1 +1], [−1 +1 −1], and [+1 −1−1] each of which has a length of
 3. 4. An apparatus for wirelesscommunication, comprising: a radio frequency (RF) unit for transmittinga radio signal; and a processor coupled to the RF unit, wherein theprocessor is configured for: generating a cyclically shifted sequence bycyclically shifting a base sequence by a cyclic shift amount; generatinga modulated sequence on the basis of a modulation symbol representing acontrol signal and the cyclically shifted sequence; generating afirst-spread sequence by spreading the modulated sequence in a firstslot by using a first orthogonal sequence; generating a second-spreadsequence by spreading the modulated sequence in a second slot by using asecond orthogonal sequence; and transmitting the first spread sequenceand the second spread sequence in the subframe that includes the firstslot and the second slot, wherein a length of the second orthogonalsequence is shorter than a length of the first orthogonal sequence, thesecond orthogonal sequence is generated by removing at least one elementincluded in the first orthogonal sequence, and the at least one elementto be removed is identical in every index of the first orthogonalsequence, and wherein the length of the first orthogonal sequence is 4,and the length of the second orthogonal sequence is 3.